大象传媒

Host Eric Robson and the panel are at Leicester University and Botanic Gardens. Answering questions from a local gardening audience are Matt Biggs, Bob Flowerdew and Anne Swithinbank.We find out about something nasty that could be lurking in our potting compost and Chris Beardshaw explores London's longest herbaceous border

Produced by Victoria Shepherd
A Somethin' Else production for 大象传媒 Radio 4

In reference to the Japanese Knotweed story, please go to the Environment Agency for general advice on rules and regulations.

Q. We are looking for a tree to provide dappled shade in a small garden. We have considered Vilmorin Rowan or Himalayan Silver Birch. Do the panel have any other suggestions?

A. Sorbus Joseph Rock is a neat, conical-shaped tree, providing yellow flowers and brilliant autumn colour. A Prunus Maackii called Amber Beauty that has spikes of white flowers and a coppery bark that peels back. Medlars are small fruit trees with very large apple blossom type flowers and could work. Azara Microphylla can be grown as a tree and has a leaf like a Cotoneaster. The wonderful thing is that in February and March a vanilla smelling fuzz appears on the back of the leaves. Sorbus Vilmorinii would work in a small garden because it is dainty. A variety of Magnolia such as a Loebneri would suit a limited space and they don't require particular soil conditions

Q. How long will builders' sand persist within the ground and will anything grow in that area?

A. The problem with builder's sand is that it is fine whereas gardeners prefer gritty sand. The drainage will be very good in that area meaning that the soil will be quite dry. Shrubs and trees would probably cope, but bedding plants wouldn't do very well
You could excavate it and mix it with potting compost. Carry out a pH test and think about how you can use it to your advantage. It has the potential to be a very good dry garden and you could grow plants such as a Pulsatilla.

Q. How could I encourage autumn colour in an ornamental grape, specifically Vitis Coignetiae growing on a west-facing wall? Each autumn the leaves turn brown and drop off.

A. If it is growing against a wall it may not be getting enough moisture towards the end of the year. On top of watering it, you could add potash feed to stimulate it.
You could take a cutting and relocate it to a more open site. Their natural habitat is woodland, where there is plenty of space and organic matter

Q. Which plants - other than box, Lavender and Rosemary - could be used to border a vegetable patch and deter slugs and snails?

A. Borage is very prickly and it will double up as a good bee plant. Slugs and snails don't like to traverse hard paths because they are open to predators and the sunshine, so slabs could help. Southernwood, a type of Artemisia, has a lovely scent and a strong smell makes it harder for pests to detect what they are looking for. A mulch of garden lime or crushed seashells would also discourage pests. Pelleted sheep's wool is also very effective

Q. Is it advisable to get rid of the Spanish Bluebells from my garden and replace them with a native British variety? If so, how would I go about it?

A. It is a lot of work because Bluebells are very deep bulbs. You could cut back the area, repeatedly taking away the leaves. Bluebells don't have a large system from which they can grow back, so they will eventually die. Wait a few years before replanting just in case seedlings appear

Q. How should apple trees be pruned to avoid the growth of dense shoots?

If pruned in winter apple trees bounce back with lots of water shoots. These should be gradually removed during the summer to weaken the tree so that they won't grow back as strongly.
A dense tree should be thinned almost back to the branch origin. This will prevent water shoots from growing and produce a better crop of fruit.

Q. Our 100 year old indoor grapevine has always provided prolific crops. Over the past few years it has started to die back and this year we are left with only ten percent of the original. Is there anything we can do to save it?

A. This could be caused by vine weevils eating away at the roots. Use a nematode and apply it close to the stems.
It could be affected by the recent wet and cold conditions. The combination of water making the bark vulnerable and then the cold weather could have a bad affect on an old plant.
Something to encourage root growth, perhaps mulch, may encourage re-growth as a last effort.

Q. Sixteen laurels have recently been cut down on a local roundabout and what remains is a chipping and soil mix. Could the panel suggest plants that will require minimal pruning and work in these conditions?

A. Native gorse is a tough evergreen and copes in poor soils. Grasses such as Stipa gigantea or Miscanthus are low maintenance and last throughout the year. If you go for more vigorous plants they will remain manageable when in poor soil. Rake away the chippings, condition the soil and then reapply t

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